Method of preparing ore fines for sintering



' METHOD; OF PREPARING ORE FOR SINTERIN G j Bernhard Weilandt and WalterStorsberg, Hagen (Haspe), Germany, assignors to Kloeckner-HuettenwerkHaspe A. G., Hagen. (Haspe), Germany NoDrawing. ApplicationJuly 3, 1956SerialNo. 595,601

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The. invention relates to. a method of preparing ore fines, dusts; andpowders for sintering, by mixing, moistening and crumbing in mixingdevices such as mixing screws,

erly, and a major part of the dust remains in unglornerulized condition,thus impairing the sinter both qualitatively and quantitatively. In thepast, the dusts and powders obtained have been treated in large sumppits. The moistened dust is then mixed with the other ores to besintered in suitable mixing drums, screws or batch mixers, together withother additives favorable to the sintering process. In this knownmethod, however, it has been found that an intimate mixture with thewater, especially if the proportions of dust and powder are high, isvery difficult to achieve, and that after sintering, the propor tion ofunsintered or reject material increases progressively, thereby renderingthe sintering process uneconomical and reducing the quality of thesinter.

The object of the present invention is to improve known methods ofpreparing ore fines, dusts and powders for sintering so as to avoid theaforesaid disadvantages.

For this purpose, it has been necessary to find means of rapidly andintimately mixing ore fines, in particular dusts and powders, with therequired moisture, at the same time converting them into a uniformlycrumbled condition, so that upon subsequent mixing in drums, screws orbarrels, an intimate and homogeneous sintering ore mixture will beobtained, without impairing the qualitative or quantitative yield of thesintering process.

This problem is solved, according to the invention, by continuouslymoistening and crumbling each of the ingredients singly while adding thequantity of water required for the material in question, thispreliminary mixing being followed as required by mixing all theingredients together. This method according to the present invention wascompared with the conventional method in processing Folldal residueswith a granulometry of 72% under 0.2 mm. into a sintering mixture. Thesintering mixture consisted of:

Percent Folldal resid 30.77 Flue dust 23.08 Mixed ore 19.23 Wetconcentrate 19.23 Wabana to 8 mm 7.69

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The Folldal residues used in the sintering rnixturej'werei (1) Processedin conventional manner in condition as' received; a (2) Premixedaccording to the present process in a m x ingscrew, with adjustment ofoptimum moisture of 25% H O.

Percent Fosdalen concentrate 27.50 Wet concentrat 37.38 Mixed ore I9,.50 Flue dust"; v 5.96 Freya fines to 8 mm c 4.76

This sintering.mixture -was-adjusted to -15 .2% =I- I Oand 435% C at a;.s nctiqn of-rl000 rnm. of. water. Coke screenings to 10 mm. were usedas fuel. Half the coke was in grain sizes to 3, ljhe grate bedconsistedof 10-30 mm. ore. The Fosdalen concentrates were charged:

( 1) In conventional manner in condition as received;

(2) Pretreated with adjustment of optimum moisture for various periodsof time in a mixing screw, and then added to the said sintering mixture.

When the sintering mixture was made up with untreated Fosdalenconcentrates, an output of 952 tons per day was attained on a belt with42 sq. m. suction area.

By separate preliminary treatment of the Fosdalen concentrates in amoistening and mixing screw according to the present process, withadjustment of optimum moisture, a sintering output of 1198 tons per daywas attained when the concentrates had remained in the mixer for 132seconds.

A special feature of the invention is that during premixing forcontinuous intensive moistening and glomerulizing, the mixing device isheated. Thus the Folldal residues according to the first example weresubjected to a comparative test by treating in a heated mixing screw atan outside temperature of 0 C. In one test, the screw was not heated; inanother test, the screw was heated so as to bring the materials to atemperature of 35 C. As a result, the output on a sintering belt of 42sq. m. suc tion area was raised from 690 tons per day with mixing screwunheated to 800 tons per day with mixing screw heated.

Another feature of the invention consists in that, to improve moisteningand glomerulizing in the premixing operation, bauxite, residues, lime ordolomite powder are added.

The Folldal residues of the sintering mixture according to thefirst'example were processed as before. ing amounts of bauxite residuesor milk of lime were added to the Folldal residues. It was found thataddition of only 0.5% bauxite residues improved the glomerulization ofthe separately premixed Folldal residues, simultaneously adjusted tooptimum moisture. I

When the Folldal residues thus prepared were sintered in the sinteringmixture specified above, the yield of sinter was 6.5% higher as comparedto the Folldal residues not treated with bauxite residues.

When, in the same sintering mixture, the Folldal residues wereseparately adjusted to optimum moisture with Increasdrum, screw orbarrel need only bring about an intimate L mixture of the severalsubstances required for the sintering process. By this means, for givenlength of time spentin the mixing drum or the like, a more intensivemixing and glomerulizing efiect is obtained, together with The processof moistening and glomerulizing by the method of the invention in thesaid mixing device may a greater output and higher quality of sinterthan heretofore, despite a more or less elevated content of dust andpowder. The mixing device for mixing the fines and in particular thedust and powder is placed behind the bunker discharge, or ahead of theconventional mixing screw, drum or barrel. a a

It has been found that by the process according to the invention, orefines, dusts and powders can be moistened so intensively, for example ina mixing screw, that 70% of ore dust and powder under 0.2 mm. can beprocessed directly on the sintering belt in a sintering mixture, byvirtue of improved moistening and glomerulizing.

It has also' been found that premixing of ore fines, dusts and powdersis affected by the temperature of the material and the mixing device aswell as by the outside temperature. the mixing equipment should beheated to an extent depending on the outside temperature.

Toachieve efiective and intensive moistening,

be improved by adding small amounts of bauxite residues or lime anddolomite powder, or of these substances in dissolved form, as milk oflime, dolomite or bauxite sludge.

The requisite cokescreenings may advantageously also be added in advanceat the time of premixing.

What we claim is:

1. The process of preparing ore fines, dusts and powders for sinterin'gby mixing, moistening and crumbling in mixing devices, which comprisesmoistening and crumbling each of the ingredients severally, continuouslyadding the required amount of water for the particular ingredient andcontinuously crumbling the several ingredients separately in a mixingscrew and then mixing the several ingredients together.

2. In the method of claim 1, the additional step of adding materialsselected from the group consisting of dolomite, bauxite residue, limeand mixtures thereof, to each of the ingredients.

References Cited in the file of this patent UNITED STATES PATENTS1,303,411 Swart et a1 May 13, 1919 FOREIGN PATENTS 1,101,880; FranceApr. 27, 1955

1. THE PROCESS OF PREPARING ORE FINES, DUSTS AND POWDERS FOR SINTERINGBY MIXING, MOISTENING AND CRUMBLING IN MIXING DEVICES, WHICH COMPRISESMOISTENING AND CRUMBLING EACH OF THE INGREDIENTS SEVERALLY, CONTINUOUSLYADDING THE REQUIRED AMOUNT OF WATER FOR THE PARTICULAR INGREDIENT ANDCONTINUOUSLY CRUMBING THE SEVERAL INGREDIENTS SEPARATELY IN A MIXINGSCREW AND THEN MIXING THE SEVERAL INGREDIENTS TOGETHER.